Fast communication networks become more and more important in order to be able to cope with the ever growing communication load caused by an increasingly networked world. At the same time power consumption is an important factor to discriminate a product over the competition and provide cost advantages.
A network switch 150 of the prior art as shown in FIG. 1, for example Extreme Networks X670©, has via its port i an optical fiber Ethernet connection 160, 164, for example 10 Gigabit Ethernet, to a remote network device 170. The other ports of the network switch can be connected to multiple other remote network devices or other devices. Multiple signals such as video signals are streamed from network sources such as video sources over the IP network 130 to the remote network devices 170. The remote network devices 170 have the function of, for example, a H.264 video decoder or transcoder. The remote network devices 170 can also, for example, have a processing function to transform the streamed video signals to a video format compatible to a specific display interface 176, 178 or display format. The remote network device 170 can alternatively or also have a data storage function. The output of the remote network device 170 is for example a DVI (Digital Visual Interface) output for a display 180. These network devices 170 have e.g. also a display control means for example VESA DPMS (Video Electronics Standards Association—Display Power Management Signaling). Management software, here called the “controlling main program” 140, can control some of the functions of the network devices 170.
In another possible configuration as shown in FIG. 2, instead of a display 180 connected to the network device 170, an image capturing device, for example a video camera 280 is connected to the remote network device via a video interface for example IEEE 1394 or SDI or HD-SDI. The camera can be controlled via for example a USB interface. The remote network device 170 can contain for example an encoder function and is connected via an optical fiber Ethernet connection 166, 168 to the network switch 150, to stream the video images over the IP network 130 to other devices connected to the IP network 130.
In another possible configuration not shown in the drawings a computer is connected to the network device 170 via for example a DVI interface or Display Port interface.
For reasons of energy conservation, reduction of operating cost, extension of battery life time and compliance with national or international regulations, it is required that electronic equipment can be preferably put in a sleep mode when the function of that equipment is not required during some time. In the sleep mode the power consumption is substantially reduced compared to the power consumption in the normal mode. For example the power consumption of a network device 170 and its related image display 180 or image capturing device 280 can be reduced to a level of less than 1 Watt, whereas in normal operation mode the power consumption can be of several tens or hundreds of Watts.
At present there is no harmonization of the terminology to describe the power states of electronic and network equipment. The normal mode of operation is also called e.g. the on/active mode. Sleep mode is also called e.g. “standby” or e.g. “low power mode”. Also e.g. “deep sleep mode” is sometimes used to indicate lower power consumption than the sleep mode. DPMS defines e.g. four modes: 1.) normal, 2.) standby, 3.) suspended and 4.) off.
In this application for instance the normal mode 1.) is used to indicate the operations mode when the full functionality of the network devices is available. Sleep mode 2.) will preferably be used to indicate a mode of the network device and its related display or image capture device where the normal operation is suspended and the power consumption is substantial lower compared with the normal mode 1.).
Network devices to support streaming media over IP networks are required to perform processing functions, for example decoding, encoding or transcoding, or data storage functions and can be located in many remote locations, very often at locations difficult to access or not directly accessible by the user or the technicians.
In prior art document U.S. Pat. No. 8,068,433 B2 a method is described for low power operation of networked devices, where on detection that the main processor is going to sleep, the processing element enters an active state in which it performs networking operations on behalf of the main processor. And in performing these networking operations on behalf to the main processor entities of the network are not aware that the main processor has gone to sleep. In particular according to the teaching of U.S. Pat. No. 8,068,433 B2 the network connection is not lost but maintained.
In prior art document U.S. Pat. No. 8,271,808 B2 a method is described where a subordinate device can determine whether the main device is operating or stopped by determining whether or not the values of the light-receiving amount stored in the light amount register is “0” continuously for more than a predetermined period. In U.S. Pat. No. 8,271,808 B2 the system can only determine the presence or absence of the light from the main device, but can't determine whether or not the absence of light is caused by stopping operating the main device or it is caused by physically disconnecting the fiber cable.